This invention relates to a method and apparatus for forming a sinuous lead wire used for obtaining U-shaped lead wires employed in the process of producing various electronic parts such as ceramic capacitors.
FIG. 1 shows a sequence of steps for obtaining an electronic part such as a ceramic capacitor, with attention paid to the lead wires. To give a description with a ceramic capacitor taken as an example, a ceramic capacitor 1 shown at the final stage in FIG. 1 comprises a capacitor body 2, and two lead wires 3 and 4. The lead wires 3 and 4 are soldered to electrodes formed on the main surfaces of the ceramic body 2, thus forming the terminals of such ceramic capacitor 1.
The operation of obtaining such lead wires 3 and 4 involves the following steps. In the first step, a linear material lead wire 5 is prepared. The material lead wire 5 is, e.g., a soldered copper wire or iron wire. In the second step, the linear material lead wire 5 is bent into U shape. In the third step, the opposite ends of the U-shaped material lead wire 5 are bent to cross each other. In the fourth step, the capacitor body 2 is held between the cross portions of the opposite ends of the material lead wire 5 and soldering is applied thereto. In the fifth step, the material lead wire 5 is cut along a cutting line 6 to provide two separate lead wires 3 and 4.
This invention is advantageously applied to the step of bending the linear material lead wire into U shape, among the steps shown in FIG. 1.
Heretofore, to obtain the U-shaped lead wire 5 shown in FIG. 1, the following method has been performed. For example as shown in FIG. 2, a material lead wire 7 cut to a predetermined length is placed on a mold 8 and is then pressed into the mold 8 by a press pin 9 having a U-shaped front end, whereby the material lead wire 7 is deformed into U shape. Alternatively, as shown in FIG. 3, a predetermined length of material lead wire 11 is placed on a round pin 10 and a mold 12 is lowered to receive the round pin 10 therein, whereby a material lead wire 11 which is deformed into U shape is obtained.
With such conventional methods, however, it is necessary to reciprocate the press pin 9 or mold 12 and the stroke required has to be greater than the length L of the U-shaped lead wire 5 shown in FIG. 1, thus imposing limits on the formation speed. Another problem is that unless the lead wires 7 and 11 are sufficiently stretched in advance, the length L and width W of the resulting U-shaped lead wire 5 shown in FIG. 1 are not accurate. Further, with the aforesaid forming means, even if the lead wire is sufficiently stretched in advance, the spring-back makes it difficult for the width W of the U-shaped lead wire 5 to take a predetermined value.